232 
MR. J. C. AV. HUMFREY OX THE EFFECTS OF STRAIN 
strained wedge—and hence difFerences in orientation such as are seen in fig. 9 may 
arise within a single crystal. 
In cutting out the single crystals from the casting, a certain amount of local strain 
was given at the edges hy the action of the saw, and it was found, upon etching, 
that where such strain had occurred the specimen no longer exhibited a uniform 
orientation, hut that numerous small areas of different orientations had ajDpeared. 
Such a breaking of the crystals has already been mentioned as aj)pearing uj^on the 
sides of the castino; shown in fiff. 1, 'vdiere it had been sawn from the surroundino- 
metal. Some specimens also had been accidentally strained hy bending, and in these 
cases a similar l^reaking-up was visible over tlie strained area when the specimen 
was re-etched. Further experiments were therefore made to obtain more definite 
results as to the production of conp^aratively small crystals by strain. 
A specimen was carefully cut with a sharp knife from the centre of a single ciwstal 
in such a manner that as little strain as possible was given. After etching it was 
found that the orientation was uniform all throup’h. It was now bent nearly double 
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between the fingers, straightened again, and re-etched. Great changes were now 
visible over the strained area, the orientation no longer being uniform, but broken up 
into ]iumerous small areas, each with a different orientation. The P’reatest chancre 
had occurred on what had been the concave side when the specimen was bent, that 
is to say, where the metal had been subjected to compression. Figs. 10 and 11 show 
the compression and tension sides respectively of a specimen originalh' uniformly 
oriented throughout (that is to say, originally a single crystal) after it liad been 
strained in tlie manner described above and then re-etched. It will be seen that on 
the compression side a large area in the centre has been split up into numerous small 
patches of different orientations, the variety of shades within this area showing in 
a strikino- manner the extent of tlie chano’e. On the tension side two or three 
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isolated patches have appeared possessing new orientations, but the amount of change 
there has been far less than on the compression side. It is also noticeable that the 
ends wliich were not subjected to any strain have not in any way altered. When we 
look more closely into the newly oriented patches, it is seen that a great number of 
straight-line boundaries exist between them, and tliis fact is still more striking when 
we use a higher maccnification. It is then seen that in some cases the boundaries are 
quite irregular and liave lieen more or less eaten out into channels during the 
etching process, hut that in others the boundaries are straight and sharp, one 
orientation changing quite ahnqitly into the other with no such channel between 
them. In the latter cases it was also apparent that there was some distinct 
geometrical relation existing between the pits on either side of the houndarv, an 
edge of the pits on either side being always parallel to the houndaiy between. In 
many cases there were turn parts joining in a straight line, but surrounded by an 
irregular boundary. Such is the case in the newly oriented patches seen in fig. 11. 
Each otthe })atches consists of two such ])ar(:s, and the straight line between them 
